You would want to run this query multiple times to see if the same files (and drive letters) consistently show up at the top of the list. If that happens, that would be evidence that you were seeing I/O bottlenecks for that file or drive letter. You could use this to help convince your SAN engineer that your were seeing I/O issues for a particular LUN.

The last two columns in the query show the cumulative number of read and writes for the file since SQL Server was started (or since the file was created, whichever was shorter). Knowing that information would be helpful if you were trying to decide which RAID level to use for a particular drive letter.